The purpose of this study is to accurately document possible racial differentials in the prevalence of major neurologic disorders by surveying an entire country, with a biracial population of approximately 25,000. The disorders investigated include cerebral palsy, dementia, psychomotor delay, epilepsy, Parkinson's disease, essential tremor, and cerebrovascular disease. Variation in mortality rates by race and sex for the entire U.S. for the years 1971 and 1973 through 1978 were also studied for 20 categories of neurologic diseases. In addition, research protocols for neuroepidemiologic studies in developing countries have been prepared for Ecuador, Mexico, Nigeria, Peru, the People's Republic of China, Spain, and Venezuela. Pilot investigations have been successfully carried out in Ecuador, Mexico, Nigeria, Peru, and the People's Republic of China.